People describe what they felt when it struck
An earthquake measuring 5.4 has caused buildings to shake across a wide area of southern California in the US.
The epicentre was 29 miles (46km) south-east of central Los Angeles, near Chino Hills in San Bernardino County, officials said.
The quake was felt as far south as San Diego but there were no reports of any serious casualties or damage.
Offices and restaurants were evacuated, and residents reported cracks in the walls of their homes.
The US Geological Survey initially said the tremor measured up to 5.8, but later downgraded its size.
California Governor Arnold Schwarzenegger said the region had been lucky to avoid a major disaster.
"This reminds us once again that in California we have to be prepared for anything and everything," he said.
The BBC's Peter Bowes in Los Angeles said the quake initially felt like a rolling motion - followed by a sudden shaking sensation that lasted about 10 seconds.
"It was dramatic. The whole building moved," said Los Angeles County sheriff's spokesman Steve Whitmore, who was in the sheriff's Monterey Park offices east of Los Angeles.
Many other buildings swayed across central Los Angeles and office workers quickly poured out onto the streets.
"We had forgotten what a big earthquake felt like, at least I did," said seismologist Kate Hutton.
"It's a drill for the big one that's going to happen someday."
There have been no reports of power cuts in the area, although telephone services were disrupted because of a surge in demand on the network.
More than 20 aftershocks were reported following the quake, the strongest measured at 3.8.
In 1994, a 6.7 magnitude earthquake in Northridge, California, killed 72 people, injured another 9,000 and caused $25bn (£12.5bn) worth of damage in the area.